Bimetallic catalysts: Requirements for stabilizing PVP removal depend on the surface composition
•Effect of PVP removal on catalysis by bimetallic nanoparticles was studied.•Pd–Ir catalysts stabilized by PVP were tested after calcination treatments.•Ring opening activity of catalysts with Ir-rich surface does not require clean surface.•Pd-rich catalysts must be cleaned before the catalysis.
Alloy and core–shell bimetallic Pd–Ir nanoparticles stabilized by polyvinylpyrrolidone (PVP) and deposited on alumina were subjected to PVP removal via thermal treatments. Less than 25% of the PVP was removed at 200 °C calcination/375 °C reduction, while the 400 °C calcination eliminated over 95% of PVP. The treated samples were tested in the gas-phase ring opening of indane at 350 °C. The cleaning was paramount for the bimetallic catalysts with Pd-rich surfaces that only exhibited activity after 400 °C calcination, while the catalysts with Ir-rich surfaces were similarly active irrespective of the presence or absence of the PVP residuals. For the CO chemisorption, complete cleaning was required for all catalysts. The study is supported by CO-DRIFTS, CO-TPD, indane-TPD, carbon analysis, TEM, CO chemisorption and catalytic measurements, and shows that the necessity to remove PVP depends on the nature of metals in bimetallic catalysts and their surface arrangements.
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Journal: Applied Catalysis A: General - Volume 482, 22 July 2014, Pages 327–335